Refining suitable petroleum crude oils to obtain a variety of lubricating oils which function effectively in diverse environments has become a highly developed and complex art. Although the broad principles involved in refining are qualitatively understood, there are quantitative uncertainties which require considerable resort to empiricism in practical refining. Underlying these quantitative uncertainties is the complexity of the molecular constitution of the precursor crude fractions. Because these crude fractions boil above about 550.degree. F., the molecular weight of the constituents is high and these constituents display almost all conceivable structures and structure types including molecules that contain, in addition to carbon and hydrogen, metals, nitrogen, oxygen and sulfur, collectively referred to hereinbelow simply as "heteroatoms". This complexity and its consequences are referred to in "Petroleum Refinery Engineering", by W. L. Nelson, McGraw Hill Book Company, Inc., New York, N.Y. 1958 (Fourth Edition), relevant portions of this text being incorporated herein by reference for background.
The basic notion in lubricant refining is that a suitable crude oil, as shown by experience or by assay, contains a quantity of lubricant base stock oil having a predetermined set of properties such as, for example, appropriate viscosity, oxidation stability, and maintenance of fluidity at low temperatures. The process of refining to isolate that lubricant base stock currently consists of a set of subtractive unit operations which removes the unwanted components. The most important of these unit operations include distillation to recover one or more fractions boiling above about 600.degree. F., solvent refining, and dewaxing, which basically are physical separation processes in the sense that if all the separated fractions were recombined one would reconstitute the crude oil.
Other processes such as hydrofinishing or clay percolation may be used if needed to reduce the nitrogen and sulfur content or improve the color of the lubricating oil stock.
A lubricant base stock, e.g. a refined petroleum oil or high boiling synthetic oils of this invention, may be used as such as a lubricant, or it may be blended with another lubricant base stock having somewhat different properties. Or, the base stock, prior to use as a lubricant, may be compounded with one or more additives which function, for example, as antioxidants, extreme pressure additives, and V.I. improves. As used herein, the term "base stock", regardless whether or not the term is further qualified, will refer only to a hydrocarbon oil without additives.
Viscosity Index (V.I.) is a quality parameter of considerable importance for lubricating oils to be used in automotive engines and aircraft engines which are subject to wide variations in temperature. This index is a series of numbers ranging from 0 to 100 which indicate the rate of change of viscosity with temperature. A Viscosity Index of 100 indicates an oil that does not tend to become viscous at low temperature or become thin at high temperatures. Measurement of the Saybolt Universal Viscosity of an oil at 100.degree. and 210.degree. F., and referral to correlations, provides a measure of the V.I. of the oil. For purposes of the present invention, whenever V.I. is referred to it is meant the V.I. as noted in the Viscosity Index tabulations of the ASTM(D567), published by ASTM, 1916 Race St., Philadelphia Pa., or equivalent.
To prepare high V.I. automotive and aircraft oils the refiner usually selects a crude oil relatively rich in paraffinic hydrocarbons, such oils being referred to commonly as "paraffin base" or "mixed base" crudes, since experience has shown that crudes poor in paraffins, such as those commonly termed "naphthene-base" crudes, yield little or no refined stock having a V.I. above about 40. (See Nelson, supra, pages 80-81 for classifications of crude oils). Suitable stocks for high V.I. oils, however, also contain substantial quantities of waxes which result in solvent-refined lubricating oil stocks of high pour point, i.e. a pour point greater than +25.degree. F. Thus, in general, the refining of crude oil to prepare acceptable base stocks ordinarily includes dewaxing to reduce the pour point to a target value less than +25.degree. F.
Factors which include the increasing shortage of high quality crudes suitable for lubricant production, the inherent limitations imposed by the complex, variable compositions of petroleum, and the increasing demand from engine manufacturers for lubes with exceptionally high V. I. and stability, have led refiners to seek synthetic oils suitable for use as lube base stock. Illustrative of materials that have been proposed are those described in U.S. Pat. No. 4,211,665 to Pellegrini et al., which describes the preparation of transformer oils by Friedel-Crafts condensation of benzene and decene oligomers; U.S. Pat. No. 4,604,491 to Dressler et al. which describes the preparation of synthetic oil by reacting alpha olefins with naphthalene over a heterogeneous acid catalyst; and U.S. Pat. No. 4,714,794 to Yoshida et al. which describes preparation of synthetic oils by reacting naphthalene and olefins with a Friedel-Crafts catalyst. U.S. Pat. No. 3,594,320 to Orkin describes upgrading a hydrocracked mineral oil either alone or admixed with a synthetic hydrocarbon fluid by treatment with an organic peroxide. U.S. Pat. No. 4,618,737 to Chester et al. describes preparation of synthetic oils by polymerizing olefins with a zeolite catalyst and, in a second stage, treating the resulting olefin oligomer with a ditertiary-alkyl peroxide. Other patents relating to the acid-catalyzed alkylation of aromatic hydrocarbons with olefins include U.S. Pat. No. 3,808,134; U.S. Pat. No. 4,148,834; and U.S. Pat. No. 4,658,072. The above-described patents all are incorporated herein by reference for background purposes.
One of the principle problems encountered with acid catalyzed alkylation of aromatic hydrocarbons is that, in general, the catalyst is not particularly selective, making it difficult to efficiently prepare only one specific aromatic derivative. For example, it is difficult to prepare a monoalkylbenzene in good single-pass yield without forming di- and higher alkylbenzenes. Also, it is difficult to form a specific dialkylbenzene isomer, since the catalyst has the ability to readily trans-alkylate and interconvert isomers.
It is an object of this invention to provide a novel synthetic alkylaromatic lube base stock. It is a further object of this invention to provide a synthetic hydrocarbon lube base stock having an exceptionally high V.I. It is still another object of this invention to provide a process for selectively manufacturing a tailored alkylaromatic hydrocarbon oil boiling above 600.degree. F. and having an exceptionally high V.I. These and other objects will become apparent to one skilled in the art on reading this entire specification including appended claims.